<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="jquery/jquery-3.1.1.min.js"></script>
    <script type="text/javascript" src="js/style.js"></script>

    <style type="text/css">
        .important{
            font-weight: bold;
            font-size: xx-large;
        }
        .bule{
            color: blue;
        }
    </style>
</head>
<body>
    <div id="div1">这是一些文本</div>
    <div id="div2" class="bule">这是一些文本</div>
    <br>
    <button id="button1">向第一个div元素添加类</button>
    <button id="button2">向第一个div元素移除类</button>
</body>
</html>